1. Field of the Invention
This invention relates to EHT power supplies suitable, for example, though not exclusively, for cathode ray tubes (CRTs) and in particular for miniature CRTs. Another potential application is for insulation testers and the like, in which small size and low stored charge are an advantage.
2. Discussion of the Prior Art
Such a power supply conventionally includes an oscillator, running at a frequency between, typically, 20 kHz and 50 kHz, a step-up transformer and a multiplier. One known type of multiplier suitable for this application consists of several rectifier stages cascaded together. Such a circuit is known as a Cockroft-Walton multiplier.
For CRT applications where the size and weight of the CRT and its associated power supplies are to be kept to a minimum, for example in the case of helmet-mounted CRT displays for use by aircrew, there is an advantage to be gained by raising the operating frequency of the oscillator to around 1 MHz so that smaller components (particularly for the capacitors in the Cockroft-Walton multiplier) may be used.
However, operating at such high frequencies incurs certain problems. In particular, the high voltage ceramic capacitors normally used in Cockroft-Walton multipliers are too lossy when operating in this frequency region and polyester capacitors of standard design have marginal performance with regard to their voltage rating.